-
[show abstract]
[hide abstract]
ABSTRACT: The solidly mounted resonator (SMR) is composed of a piezoelectric thin film sandwiched between two electrodes and a Bragg
reflector that comprises alternating high and low acoustic impedance with a thickness of a quarter wavelength. In this study,
the combination Mo/SiO2 is chosen as high/low acoustic impedance materials to form a Bragg reflector; aluminum nitride (AlN) is utilized as the piezoelectric
layer. The purpose of this study is to investigate the resonance characteristics of solidly mounted resonators with various
pairs of reflecting layers. The experimental results yield an electromechanical coupling
(keff2)(k_{\mathrm{eff}}^{2})
of 1.926% and quality factor (Q) of 254 with three pairs of Mo/SiO2 layers. The figure of merit (FOM), which is defined as the product of electromechanical coupling and quality factor, has
a maximum of 489 with three pairs of Mo/SiO2 layers.
Applied Physics A 04/2012; 99(1):271-278. · 1.63 Impact Factor
-
Chung-Jen Chung,
Po-Tsung Hsieh,
Jen-Fin Lin,
Ching-Liang Wei,
Wei-Tsai Chang,
Cheng-Ting Chen,
Ying-Chung Chen, Chien-Chuan Cheng,
Cheng-Hsiang Lin,
Kuo-Chih Chiu,
Shean-Jen Chen,
Kuo-Sheng Kao
[show abstract]
[hide abstract]
ABSTRACT: In this study, two approach of the molecular-level detection technique, acoustic-based and Raman-scattering-based detection, are adopted. The acoustic resonant signals are sensitive to the loading mass, such as nano particles and bio-molecules, while Raman scattering signals are highly surface sensitive to a wide range of adsorbate molecules. Aluminum nitride (AlN) thin film dominars both of the techniques. In the acoustic device, AlN acts as a piezoelectric layer to excite acoustic wave. In the Raman scattering experiment, the surface morphology of AlN give rise to a surface enhanced Raman signal. Thus, thin film bulk acoustic wave (TFBAW) properties as well as the surface enhanced Raman spectroscopy (SERS) signals of AlN are investigated. To obtain good piezoelectricity, a highly c-axis orientated AlN thin film is prepared by a reactive RF magnetron sputtering system. The c-axis orientated AlN possesses a pebble-like morphology, which is suitable for the SERS. Solidly-mounted resonators (SMR) are adopted to excite high frequency resonant signal, and the 1.5 GHz shear resonance signal is obtained. In the SERS measurement, the aqueous solution of Rhodamine 6G with concentration of 10 -6 M added with 10 mM of sodium chloride
01/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: Proton exchange (PE) is an attractive method for the fabrication of optical and acoustic waveguides in lithium niobate (LiNbO3). LiNbO3 substrate has large electromechanical coupling coefficient (K2) and moderate SAW velocity, but its temperature coefficient of frequency (TCF) is as large as -73 ppm/°C. Silicon dioxide (SiO2) is a well-known non-piezoelectric material having the positive TCF for SAW. The SiO2 thin films are deposited on the PE-LiNbO3 substrates to improve the TCF of the SAW devices. The results show that the temperature stability of SAW on SiO2/PE-LiNbO3 substrate is improved to be about -55 ppm/°C.
Ferroelectrics 09/2010; 2004(Vol. 304):143-145. · 0.39 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study investigates c-axis tilted aluminum nitride (AlN) piezoelectric films for the improvement of both shear and longitudinal
acoustic wave resonances. Solidly-mounted resonator (SMR) structure is adopted for the applications of high frequency wireless
communications and high sensitivity sensors. As to the piezoelectric layer, c-axis tilted AlN has the capability to excite
the dual-mode resonances, namely, the longitudinal and shear mode resonances. In this study, SMR devices made with a seven-layer
molybdenum/silicon dioxide (Mo/SiO2) Bragg reflector and the c-axis tilted AlN are carried out. A conventional off-axis sputtering technique is applied to grow
the tilted AlN.
The outcome frequency responses show dual resonant characteristics. However, the longitudinal resonance fades away with the
AlN c-axis tilted angle, and the quality factor of the longitudinal resonance decreases. Consequently, we make an improvement
by tilting the off-center substrates toward the sputtering source and successfully enhance the longitudinal resonance while
preserving the shear resonance at the same time. Not only the shear resonance for the liquid-based sensing application, but
also an outstanding longitudinal resonance could be obtained. The practicability of the dual-mode resonator is extended.
Applied Physics A 01/2009; 94(2):307-313. · 1.63 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The solidly mounted resonator (SMR) is composed of a piezoelectric AlN thin film sandwiched between two electrodes and a Bragg reflector consisting of alternating high and low acoustic impedance layers of quarter-wavelength thickness. According to the different arrangements of high and low acoustic impedance layers, SMR devices form two resonance modes, i.e. 1/2 lambda and 1/4 lambda mode configurations. The purpose of this study is to compare the resonance characteristics of these two configurations. The thickness of the piezoelectric layer for 1/4 lambda mode configuration is set equal to a half of that for 1/2 lambda mode configuration. Therefore, the piezoelectric thin film for 1/2 lambda mode configuration exhibits better crystallization owing to its film thickness. It leads to a high coupling coefficient, k<sup>2</sup>, and a wide bandwidth if piezoelectric thin film is fabricated with good crystalline characteristics. As to 1/4 lambda mode configuration with moderate film thickness, it has a better surface smoothness and a lower stress resulting in a slight scattering of the acoustic wave. As a result, the SMR device with 1/4 lambda mode configuration leads to a high quality factor. The return loss outside passband is obviously close to zero for the 1/4 lambda mode configuration.
Frequency Control Symposium, 2008 IEEE International; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: The concept of the solidly mounted resonator (SMR) structure was introduced in 1965. A SMR consists of a multi-layered structure and requires material interfaces that confine waves to resonate as standing waves. Thin piezoelectric films such as AlN and ZnO with tilted texture have the capability to excite the dual mode resonance, namely, the longitudinal and shear mode resonance. To grow the tilted AlN, the substrate is placed at a variable distance from the substrate holder center in a reactive magnetron sputtering system. In addition, we tilt the off-center substrates toward the sputtering source in order to reduce the acoustic energy loss of the longitudinal wave and preserve the shear mode resonance at the same time. In this study, the 1/4 lambda mode SMR devices made with a seven-layer Mo/SiO<sub>2</sub> Bragg reflector and the c-axis tilted AlN are carried out. The Bragg reflector is optimized deposited with 2.28 nm RMS surface roughness, and the AlN is sputtered in appropriate sputtering pressure and appropriate substrate temperature to promote the growth of both the highly c-axis orientated and tilted AlN. The off-center deposition method evolves in a competitive growth bringing about an AlN growth pivoted in the ion-flux direction. The outcome frequency responses show dual resonant characteristics around 1.4 GHz and 2.5 GHz resulted from the shear and longitudinal resonances, respectively. We successfully improve the longitudinal resonance by tilting the substrate toward the sputtering source. Not only the shear resonance for the liquid media sensing application, but also an outstanding longitudinal resonance could be obtained. The superior dual mode resonances are realized.
Frequency Control Symposium, 2008 IEEE International; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: In this study, platinum (Pt) and zinc oxide (ZnO) had been adopted as electrode and piezoelectric layer of FBAR resonator. There are several types of filters, such as ladder-type, lattice-type and stacked couple filter, constructed from the FBAR resonator. The T-ladder type filter had been elected because of its high quality and simple fabrication processes. The pass-band width of filter is controlled by the mass loading on the specific resonator. The resonant frequency of FBAR is decided by the thickness of the piezoelectric layer. Due to the off-axis deposition, a dual mode resonance phenomenon is appeared. The precise mass loading is critical for the pass-band competition of longitude mode and shear mode in dual band filter. The frequency response is measured using an HP8720 network analyzer and a CASCADE probe station. The center frequency, 3-dB bandwidth, insertion loss and band rejection of longitude mode are 2353.125 MHz, 76.2 MHZ, -4.8066 dB and 7.1308 dB respectively. The center frequency, 3-dB bandwidth, insertion loss and band rejection of shear mode are 1044.375 MHz, 22.975 MHZ, -8.8314 dB and 1.5 dB respectively. The device has achieved and has a chance to apply in dual band wireless communication system.
Frequency Control Symposium, 2008 IEEE International; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: This study focused on the fabrication and the theoretical analysis of solidly mounted resonators (SMR) concerning dual-mode frequency responses and their frequency shift of bulk acoustic wave (BAW) resonance. For this device fabrication, RF/DC magnetron sputtering and photolithography were employed to constitute the required multilayer structure. For the theoretical analysis, the dualmode frequency shift was characterized by the Sauerbrey's formula, and a modified formula was carried out following the trend for the large frequency shift. In the fabrication of the SMR device, Mo/SiO2 was chosen to construct the Bragg reflector as the high/low acoustic impedance materials, respectively, and aluminum nitride (AlN) was used as a piezoelectric layer. To investigate the characteristics of BAW on the dual-mode frequency shift, the c-axis tilted angle of AlN was altered as well as the various mass loading on the SMR. Based on the experimental results, the dual-resonance frequencies showed a nonlinear decreasing trend with a linear increase of the mass loading. Therefore, a modified formula was carried out. Furthermore, the ratio of the longitudinal-resonant frequency to the shear-resonant frequency remained at a range around 1.76 despite the various c-axis tilted angles of AlN and gradual mass loading on the SMR. The electromechanical coupling coefficient, k2(eff), of the shear resonance rose with the increase of the c-axis tilted angle of AlN.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 05/2008; 55(4):857-64. · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The fabrication and frequency responses of solidly mounted resonators (SMRs) consisting of a single layer of aluminum nitride
(AlN) piezoelectric thin film, and varying numbers of multi-layered titanium/molybdenum (Ti/Mo) thin films has been investigated.
In order to obtain the frequency response near 2.5GHz, specific thicknesses of AlN, Mo, and Ti were designed for the thin
film deposition processes. Manufacturing parameters of thin films in the sputtering system, such as deposition power, temperature
and pressure, were adjusted to obtain the optimum surface roughness of 13.9nm for four-pair Ti/Mo. The SMR devices with various
numbers of Ti/Mo pairs were investigated and the frequency responses were compared. The SMR devices showed the distinct resonant
phenomenon with excellent sidelobe suppression at 2.31GHz. The more Ti/Mo pairs, the better the frequency characteristics
obtained. The experimental results revealed that the Ti/Mo Bragg reflector exhibits an excellent property to restrain acoustic
dissipation caused by the substrate, and is suitable for the fabrication of SMR devices.
Applied Physics A 01/2008; 90(3):501-506. · 1.63 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The solidly mounted resonator (SMR) is fabricated using planar processes from a piezoelectric layer sandwiched between two electrodes upon Bragg reflectors, which then are attached to a substrate. To transform the effective acoustic impedance of the substrate to a near zero value, the Bragg reflectors are composed of alternating high and low acoustic impedance layers of quarter-wavelength thickness. This paper presents the influence of Bragg reflector surface roughness on the resonance characteristics of an SMR. Originally, an A1N/A1 multilayer is used as the Bragg reflector. The poor surface roughness of this Bragg reflector results in a poor SMR frequency response. To improve the surface roughness of Bragg reflectors, a molybdenum (Mo)/titanium (Ti) multilayer with a similar coefficient of thermal expansion is adopted. By controlling deposition parameters, the surface roughness of the Bragg reflector is improved, and better resonance characteristics of SMR are obtained.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 05/2007; 54(4):802-8. · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A nontoxic proton source, octanoic acid, was adopted to fabricate proton-exchanged (PE) waveguides in 36° Y-X lithium tantalate (LiTaO<sub>3</sub>) substrates. The PE ability of octanoic acid on LiTaO<sub>3</sub>, the penetration depth, was investigated by secondary-ion mass spectrometry (SIMS). The penetration depth of hydrogen ion exhibited an obviously step-like profile, which will be excellent for waveguide application. The relationship between waveguide depth (d) and exchanging time (t) was represented by d = 0.0653 × √t at T = 200°C. To deserve to be mentioned, the octanoic acid has a slight dissociation coefficient and low activation energy, thus the accurate waveguide depth control can be obtained. For the application of acoustic wave guided acousto-optic devices, the leaky surface acoustic wave (LSAW) properties of PE 36° Y-X LiTaO<sub>3</sub> waveguides were investigated. The phase velocity slightly decreased with the increase of kd, where k was wavenumber. An indispensable parameter of acoustic wave device, the temperature coefficient of frequency (TCF), calculated from the frequency change of the output of LSAW delay line showed an increase with increased kd.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2006; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Surface acoustic wave (SAW) properties of proton-exchanged (PE) z-cut lithium niobate (LiNbO/sub 3/) waveguides with silicon dioxide (SiO/sub 2/) film layers were investigated using octanoic acid. The distribution of hydrogen measured by secondary ion mass spectrometry (SIMS) showed a step-like profile, which was assumed to be equal to the waveguide depth (d). The SiO/sub 2/ film was deposited on z-cut LiNbO/sub 3/ waveguide by radio frequency (rf) magnetron sputtering. We investigated the important parameters for the design of SAW devices such as phase velocity (V/sub p/), insertion loss (IL) and temperature coefficient of frequency (TCF) by a network analyzer using thin-film aluminum interdigital transducer electrodes on the upper SiO/sub 2/ film surface. The experimental results showed that the V/sub p/ of SAW decreased slightly with the increase of h//spl lambda/, where h was the thickness of SiO/sub 2/ films and /spl lambda/ was the wavelength. The IL of SAW increased with increased h//spl lambda/. The TCF of SAW calculated from the frequency change of the output of SAW delay line showed an evident decrease with the increase of h//spl lambda/. The TCF for PE z-cut LiNbO/sub 3/ was measured to be about -54.72 ppm//spl deg/C at h//spl lambda/ = 0.08. It revealed that the SiO/sub 2/ films could compensate and improve the temperature stability as compared with the TCF of SAW on PE samples without SiO/sub 2/ film.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 04/2005; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Surface acoustic wave (SAW) properties of proton-exchanged (PE) z-cut lithium niobate (LiNbO3) waveguides with silicon dioxide (SiO2) film layers were investigated using octanoic acid. The distribution of hydrogen measured by secondary ion mass spectrometry (SIMS) showed a step-like profile, which was assumed to be equal to the waveguide depth (d). The SiO2 film was deposited on z-cut LiNbO3 waveguide by radio frequency (rf) magnetron sputtering. We investigated the important parameters for the design of SAW devices such as phase velocity (Vp), insertion loss (IL) and temperature coefficient of frequency (TCF) by a network analyzer using thin-film aluminum interdigital transducer electrodes on the upper SiO2 film surface. The experimental results showed that the Vp of SAW decreased slightly with the increase of h/lambda, where h was the thickness of SiO2 films and lambda was the wavelength. The IL of SAW increased with increased h/lambda. The TCF of SAW calculated from the frequency change of the output of SAW delay line showed an evident decrease with the increase of h/lambda. The TCF for PE z-cut LiNbO3 was measured to be about -54.72 ppm/degreees C at h/lambda = 0.08. It revealed that the SiO2 films could compensate and improve the temperature stability as compared with the TCF of SAW on PE samples without SiO2 film.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 04/2005; 52(3):503-6. · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Proton exchange (PE) is an attractive method for the fabrication of optical and acoustic waveguides in lithium tantalite (LiTaO<sub>3</sub>) substrate. Octanoic acid was used for the fabrication of PE LiTaO<sub>3</sub> waveguides. After the PE process, the resultant substrate showed a damage-free surface from observations by scanning electron microscopy (SEM). And X-ray diffraction (XRD) was adopted to identify the crystalline structure of LiTaO<sub>3</sub>. From the X-ray diffraction (XRD) results, the reflection peak of (306) was shifted after the PE process. The influences of the exchanging time on properties of leaky surface acoustic wave (LSAW) devices were discussed. The single electrode geometry of interdigital transducers (IDT) was adopted to excite and receive the acoustic wave. The wavelength (λ) of the LSAW is 32 μm. The frequency response of the LSAW is measured using an HP 8720ET network analyzer. The velocity of LSAW was decreased as the increase of PE time; nevertheless, the range of variation was quite small. Measurements of the temperature dependence of LSAW velocity were carried in the temperature range from 0°C to 80°C. The temperature coefficient of frequency (TCF) of LSAW devices was significantly increased by the increase of PE time. The PE process changed the characteristics of material and specific property can be obtained.
Ultrasonics Symposium, 2004 IEEE; 09/2004
-
[show abstract]
[hide abstract]
ABSTRACT: The surface acoustic wave (SAW) propagation characteristics of a layered structure consisting of a SiO<sub>2</sub> thin film on z-cut LiNbO<sub>3</sub> substrate in company with temperature dependence of frequency of this structure has been studied experimentally. The temperature coefficient of frequency (TCF) of SAW devices was obtained by a network analyzer. A SAW device on the lithium niobate (LiNbO<sub>3</sub>) exhibits a large negative TCF. It revealed that the SiO<sub>2</sub> thin film was introduced as compensation layer for improving the temperature stability. The TCF of the SiO<sub>2</sub>/LiNbO<sub>3</sub> based structure was significantly decreased due to the SiO<sub>2</sub> thin film deposition. The TCF of SAW on the SiO<sub>2</sub>/LiNbO<sub>3</sub> device was measured to be about -51 ppm/°C at h/λ=0.12, where h was the thickness of SiO<sub>2</sub> film and λ was the wavelength of SAW. It indicated that the SiO<sub>2</sub> thin film deposited on LiNbO<sub>3</sub> substrate could improve the temperature stability, as compared with the TCF of SAW on bare LiNbO<sub>3</sub>. Furthermore, the phase velocity (V<sub>p</sub>) of SAW on SiO<sub>2</sub>/LiNbO<sub>3</sub> substrate was not altered by the increase of SiO<sub>2</sub> thickness (h/λ).
Ultrasonics Symposium, 2004 IEEE; 09/2004
-
[show abstract]
[hide abstract]
ABSTRACT: Highly c-axis prefer-oriented aluminum nitride (AlN) thin films deposited on the Y-rotated, X-propagating, (ST-X), cut of quartz substrates were obtained by reactive rf magnetron sputtering to investigate the temperature coefficient of frequency (TCF) for surface acoustic wave (SAW) devices. The experimental results show that the slope of the temperature dependence of the center frequency of the SAW device on ST-X quartz substrate was doubtless zero and the TCF was calculated to be 0 ppm/°C. As compared, with AlN film on ST-X quartz, the TCF was measured to be about 16 ppm/°C with h/λ=0.05, where h was the AIN film thickness and λ was the wavelength of SAW. The AlN/ST-X quartz based structure could also improve the acoustic wave velocity of SAW devices.
Ultrasonics Symposium, 2002. Proceedings. 2002 IEEE; 11/2002
-
[show abstract]
[hide abstract]
ABSTRACT: The c-axis-oriented aluminum nitride (AIN) films were deposited on z-cut lithium niobate (LiNbO3) substrates by reactive RF magnetron sputtering. The crystalline orientation of the AIN film determined by x-ray diffraction (XRD) was found to be dependent on the deposition conditions such as substrate temperature, N2 concentration, and sputtering pressure. Highly c-axis-oriented AIN films to fabricate the AIN/LiNbO3-based surface acoustic wave (SAW) devices were obtained under a sputtering pressure of 3.5 mTorr, N2 concentration of 60%, RF power of 165 W, and substrate temperature of 400 degrees C. A dense pebble-like surface texture of c-axis-oriented AIN film was obtained by scanning electron microscopy (SEM). The phase velocity and the electromechanical coupling coefficient (K2) of SAW were measured to be about 4200 m/s and 1.5%, respectively. The temperature coefficient of frequency (TCF) of SAW was calculated to be about -66 ppm/ degrees C.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 04/2002; 49(3):345-9. · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The c-axis-oriented aluminum nitride (AlN) films were deposited on z-cut lithium niobate (LiNbO/sub 3/) substrates by reactive RF magnetron sputtering. The crystalline orientation of the AlN film determined by x-ray diffraction (XRD) was found to be dependent on the deposition conditions such as substrate temperature, N/sub 2/ concentration, and sputtering pressure. Highly c-axis-oriented AlN films to fabricate the AlN/LiNbO/sub 3/-based surface acoustic wave (SAW) devices were obtained under a sputtering pressure of 3.5 mTorr, N/sub 2/ concentration of 60%, RF power of 165 W, and substrate temperature of 400/spl deg/C. A dense pebble-like surface texture of c-axis-oriented AlN film was obtained by scanning electron microscopy (SEM). The phase velocity and the electromechanical coupling coefficient (K/sup 2/) of SAW were measured to be about 4200 m/s and 1.5%, respectively. The temperature coefficient of frequency (TCF) of SAW was calculated to be about -66 ppm//spl deg/C.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 04/2002; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The proton-exchanged (PE) and annealed PE (APE) z-cut LiNbO/sub 3/ waveguides were fabricated using H/sub 4/P/sub 2/O/sub 7/. The positive strain, c-axis lattice constant change (/spl Delta/c/c), was calculated to be about +0.43%, which was almost independent of the exchanged conditions. The penetration depth of H measured by secondary ion mass spectrometry (SIMS) exhibited a step-like profile, which was assumed to be equal to the waveguide depth (d). The surface acoustic wave (SAW) properties of PE and APE z-cut LiNbO/sub 3/ samples were investigated. The phase velocity (V/sub p/) and electromechanical coupling coefficient (K/sup 2/) of PE samples were significantly decreased by the increase of kd, where k was the wavenumber (2/spl pi///spl lambda/). The insertion loss (IL) of PE samples was increased by the increase of kd and became nearly constant at kd>0.064. The temperature coefficient of frequency (TCF) of PE samples allowed an apparent increase with kd, reaching a maximum at kd=0.292, then slightly decreased at higher kd. The effects of annealing resulted in a restoration of V/sub p/ and an improvement of IL.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 04/2001; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Highly c-axis oriented aluminum nitride (AlN) films were deposited
on z-cut LiNbO<sub>3</sub> substrates by reactive rf magnetron
sputtering. Growth behaviors of the AlN films deposited at various
deposition conditions such as sputtering pressure, nitrogen
concentration and substrate temperature were investigated. The
crystalline orientation of the AlN film was determined by x-ray
diffraction (XRD) which was sensitive to the deposition conditions. A
dense pebble-like surface texture of c-axis oriented AlN film was
obtained by scanning electron microscopy (SEM). The cross section of
c-axis oriented AlN film showed a high degree of alignment of the
columnar structure. A network analyzer was used to measure the surface
acoustic wave (SAW) characteristics. The phase velocity and the
electromechanical coupling coefficient were calculated to be about 4200
m/sec and 1.5%, respectively
Applications of Ferroelectrics, 2000. ISAF 2000. Proceedings of the 2000 12th IEEE International Symposium on; 02/2000
